The present invention relates to conserving and moving substrates such as semiconductor wafers or masks in cleanrooms, between the various working steps to which substrates are subjected in processes for fabricating semiconductors and microelectronic mechanical systems (MEMS).
In the fabrication of semiconductors and MEMS, substrates such as silicon wafers or masks are transported in mini-environment enclosures which protect them from the pollution still present in the atmosphere of a cleanroom.
At present, silicon wafers having a diameter of 200 millimeters (mm) are transported in bottom-opening enclosures generally referred to as standard mechanical interface (SMIF) pods.
Silicon wafers having a diameter of 300 mm are transported in front-opening enclosures that are generally referred to as standardized front-opening universal pods (FOUPs).
Mini-environment enclosures have also been devised that are adapted for transporting a single substrate wafer.
Semiconductor wafers or other wafers typically remain for several weeks in a semiconductor fabrication unit between the various process steps. During this time, semiconductor or other wafers need to be protected against any risk of pollution, and that is why provision is made to isolate them from the atmosphere in clean-rooms, by transporting them and conserving them in mini-environment enclosures.
A mini-environment enclosure must be disconnected from any external source of energy while it is being moved between various workstations. During this period, the mini-environment enclosure must itself be capable of maintaining the controlled atmosphere around the substrate it contains. This requires a source of energy to be available in the mini-environment enclosure, and a pumping system for maintaining the controlled atmosphere which is at very low pressure, i.e. a pressure of the same order as the pressures that exist in the transfer and loading chambers leading to process chambers.
In recent standards in force in the fabrication of semiconductors, the semiconductor wafer to be protected is generally conserved with the active face of the wafer facing upwards, however masks can be conserved with an active face facing either upwards or else downwards. For example, masks for extreme ultraviolet (EUV) etching have their active faces facing downwards. It is then necessary to have a mini-environment enclosure that is capable of being compatible with a substrate being positioned with its active face either facing upwards or else facing downwards, and that is compatible with the conditioning stations to which mini-environment enclosures can be coupled for long-duration storage, and which is compatible with the inlet/outlet structures leading to the transfer chambers and the loading chambers of process chambers.
Thus, a first problem addressed by the invention is to design a mini-environment enclosure that provides the substrate it contains with effective protection while still being easily compatible both with a substrate having its active face facing upwards and with a substrate having its active face facing downwards. Compatibility must be ensured in a manner that is simple and inexpensive.
A second problem addressed by the invention is to design a mini-environment enclosure that presents size that is sufficiently compact and endurance that is sufficiently long to maintain the controlled atmosphere during steps of transporting the substrate and possibly also during steps of storing the substrate for an appropriate duration.
The invention thus provides apparatus for transporting substrates under a controlled atmosphere, the apparatus comprising a mini-environment enclosure with an internal cavity.